Attempts have been made to incorporate integral handles in PET and like injection blow moulded containers—for example see U.S. Pat. No. 4,629,598 to Thompson, assigned to Tri-Tech Systems International, Inc. The parison from which the handled bottles of U.S. Pat. No. 4,629,598 are produced is illustrated in FIG. 1. To date, however, attempts to produce a practical, mass produced version of this arrangement have been unsuccessful. Instead, the best that appears to have been done in commercial practice is an arrangement whereby the blown containers are arranged to accept a clip on or snap on handle in a separate production step after the container itself is formed. See for example WO82/02371 and WO82/02370, both to Thompson.
Injection-stretch-blow moulding is a process in which the parison is stretched both axially and radially, resulting in biaxial orientation.
Biaxial orientation provides increased tensile strength (top load), less permeation due to tighter alignment of the molecules, and improved drop impact, clarity, and lightweighting of the container.
Not all thermoplastics can be oriented. The major thermoplastics used are polyethylene terephthalate (PET), polyacrylonitrile (PAN), polyvinyl chloride (PVC), and polypropylene (PP). PET is by far the largest volume material, followed by PVC, PP, and PAN.
The amorphous materials, e.g., PET, with a wide range of thermoplasticity are easier to stretch-blow than the partially crystalline types such as PP. Approximate melt and stretch temperatures to yield maximum container properties are:
MaterialMelt, Degrees C.Stretch, Degrees C.PET280107PVC180120PAN210120PP240160
There are basically two types of processes for stretch-blow moulding: 1) single-stage in which preforms are made and bottles blown on the same machine, and 2) two-stage in which preforms are made on one machine and blown later on another machine.
Single-stage equipment is capable of processing PVC, PET, and PP. Once the parison is formed (either extruded or injection moulded), it passes through conditioning stations which bring it to the proper orientation temperature. The single-stage system allows the process to proceed from raw material to finished product in one machine, but since tooling cannot be easily changed, the process is best suited for dedicated applications and low volumes.
Oriented PVC containers most commonly are made on single-stage, extrusion-type machines. The parison is extruded on either single- or double-head units. Temperature conditioning, stretching, and thread forming are done in a variety of ways depending on the design of the machine. Many of the processes presently in use are proprietary.
Many oriented PET containers are produced on single-stage machines. Preforms are first injection moulded, then transferred to a temperature conditioning station, then to the blow moulding operation where the preforms are stretch-blown into bottles, and finally to an eject station.
With the two-stage process, processing parameters for both preform manufacturing and bottle blowing can be optimized. A processor does not have to make compromises for preform design and weight, production rates, and bottle quality as he does on single-stage equipment. He can either make or buy preforms. And if he chooses to make them, he can do so in one or more locations suitable to his market. Both high-output machines and low output machines are available. Two stage extrusion-type machines generally are used to make oriented PP bottles. In a typical process, preforms are re-extruded, cooled, cut to length, reheated, stretched while the neck finish is being trimmed, and ejected. The two-stage process is the lowest-cost method to produce oriented PET containers. The two-stage process, which permits injection moulding of the preform and then shipping to blow moulding locations, has allowed companies to become preform producers and to sell to blow moulding producers. Thus companies that wish to enter the market with oriented PET containers can minimise their capital requirements. Two-stage stretch-blow moulding also is being used for production of oriented PVC containers. Preform design and its relationship to the final container remains the most critical factor. The proper stretch ratios in the axial and hoop directions must be met if the container is to properly package its intended product.
MaterialStretch RatiosOrientation Temp. Deg. F.PET16/1 195-240PVC7/1210-240PAN9/1220-260PP6/1260-280
It is an object of the present invention to produce a practical, readily implementable injection, stretch blow moulded container made from an orientable thermoplastics material incorporating a handle which is formed during and as part of the said injection, stretch blow moulding operation.